This invention relates, in general, to softening tissue paper; and more specifically, to a composition which may be applied to the surface of tissue paper for enhancing the softness thereof.
Sanitary paper tissue products are widely used. Such items are commercially offered in formats tailored for a variety of uses such as facial tissues, toilet tissues and absorbent towels.
All of these sanitary products share a common need, specifically to be soft to the touch. Softness is a complex tactile impression evoked by a product when it is stroked against the skin. The purpose of being soft is so that these products can be used to cleanse the skin without being irritating. Effectively cleansing the skin is a persistent personal hygiene problem for many people. Objectionable discharges of urine, menses, and fecal matter from the perineal area or otorhinolaryngogical mucus discharges do not always occur at a time convenient for one to perform a thorough cleansing, as with soap and copious amounts of water for example. As a substitute for thorough cleansing, a wide variety of tissue and toweling products are offered to aid in the task of removing from the skin and retaining such discharges for disposal in a sanitary fashion. Not surprisingly, the use of these products does not approach the level of cleanliness that can be achieved by the more thorough cleansing methods, and producers of tissue and toweling products are constantly striving to make their products compete more favorably with thorough cleansing methods.
Shortcomings in tissue products for example cause many to stop cleaning before the skin is completely cleansed. Such behavior is often prompted by the harshness of the tissue, as continued rubbing with a harsh implement can abrade the sensitive skin and cause severe pain. The alternative, leaving the skin partially cleansed, is chosen even though this often causes malodors to emanate and can cause staining of undergarments, and over time can cause skin irritations as well.
Disorders of the anus, for example hemorrhoids, render the perianal area extremely sensitive and cause those who suffer such disorders to be particularly frustrated by the need to clean their anus without prompting irritation.
Another notable case which prompts frustration is the repeated nose blowing necessary when one has a cold. Repeated cycles of blowing and wiping can culminate in a sore nose even when the softest tissues available today are employed.
Accordingly, making soft tissue and toweling products which promote comfortable cleaning without performance impairing sacrifices has long been the goal of the engineers and scientists who are devoted to research into improving tissue paper. There have been numerous attempts to reduce the abrasive effect, i.e., improve the softness of tissue products.
One area that has been exploited in this regard has been to select and modify cellulose fiber morphologies and engineer paper structures to take optimum advantages of the various available morphologies. Applicable art in this area includes: Vinson et. al. in U.S. Pat. No. 5,228,954, issued Jul. 20, 1993, Vinson in U.S. Pat. No. 5,405,499, issued Apr. 11, 1995, Cochrane et al. in U.S. Pat. No. 4,874,465 issued Oct. 17, 1989, and Hermans, et. al. in U.S. Statutory Invention Registration H1672, published on Aug. 5, 1997, all of which disclose methods for selecting or upgrading fiber sources to tissue and toweling of superior properties. Applicable art is further illustrated by Carstens in U.S. Pat. No. 4,300,981, issued Nov. 17, 1981, which discusses how fibers can be incorporated to be compliant to paper structures so that they have maximum softness potential. While such techniques as illustrated by these prior art examples are recognized broadly, they can only offer some limited potential to make tissues truly effective comfortable cleaning implements.
Another area which has received a considerable amount of attention is the addition of chemical softening agents (also referred to herein as xe2x80x9cchemical softenersxe2x80x9d) to tissue and toweling products.
As used herein, the term xe2x80x9cchemical softening agentxe2x80x9d refers to any chemical ingredient which improves the tactile sensation perceived by the consumer who holds a particular paper product and rubs it across the skin. Although somewhat desirable for towel products, softness is a particularly important property for facial and toilet tissues. Such tactilely perceivable softness can be characterized by, but is not limited to, friction, flexibility, and smoothness, as well as subjective descriptors, such as a feeling like lubricious, velvet, silk or flannel. Suitable materials include those which impart a lubricious feel to tissue. This includes, for exemplary purposes only, basic waxes such as paraffin and beeswax and oils such as mineral oil and silicone oil as well as petrolatum and more complex lubricants and emollients such as quaternary ammonium compounds with long alkyl chains, functional silicones, fatty acids, fatty alcohols and fatty esters.
The field of work in the prior art pertaining to chemical softeners has taken two paths. The first path is characterized by the addition of softeners to the tissue paper web during its formation either by adding an attractive ingredient to the vats of pulp which will ultimately be formed into a tissue paper web, to the pulp slurry as it approaches a paper making machine, or to the wet web as it resides on a Fourdrinier cloth or dryer cloth on a paper making machine.
The second path is categorized by the addition of chemical softeners to tissue paper web after the web is dried. Applicable processes can be incorporated into the paper making operation as, for example, by spraying onto the dry web before it is wound into a roll of paper.
Exemplary art related to the former path categorized by adding chemical softeners to the tissue paper prior to its assembly into a web includes U.S. Pat. No. 5,264,082, issued to Phan and Trokhan on Nov. 23, 1993, incorporated herein by reference. Such methods have found broad use in the industry especially when it is desired to reduce the strength which would otherwise be present in the paper and when the papermaking process, particularly the creping operation, is robust enough to tolerate incorporation of the bond inhibiting agents. However, there are problems associated with these methods, well known to those skilled in the art. First, the location of the chemical softener is not controlled; it is spread as broadly through the paper structure as the fiber furnish to which it is applied. In addition, there is a loss of paper strength accompanying use of these additives. While not being bound by theory, it is widely believed that the additives tend to inhibit the formation of fiber to fiber hydrogen bonds. There also can be a loss of control of the sheet as it is creped from the Yankee dryer. Again, a widely believed theory is that the additives interfere with the coating on the Yankee dryer so that the bond between the wet web and the dryer is weakened. Prior art such as U.S. Pat. No. 5,487,813, issued to Vinson, et. al., Jan. 30, 1996, incorporated herein by reference, discloses a chemical combination to mitigate the before mentioned effects on strength and adhesion to the creping cylinder; however, there still remains a need to incorporate a chemical softener into a paper web in a targeted fashion with minimal effect on web strength and interference with the production process.
Further exemplary art related to the addition of chemical softeners to the tissue paper web during its formation includes U.S. Pat. No. 5,059,282, issued to Ampulski, et. al. on Oct. 22, 1991 incorporated herein by reference. The Ampulski patent discloses a process for adding a polysiloxane compound to a wet tissue web (preferably at a fiber consistency between about 20% and about 35%). Such a method represents an advance in some respects over the addition of chemicals into the slurry vats supplying the papermaking machine. For example, such means target the application to one of the web surfaces as opposed to distributing the additive onto all of the fibers of the furnish. However, such methods fail to overcome the primary disadvantages of the addition of chemical softeners to the wet end of the papermaking machine, namely the strength effects and the effects on the coating of the Yankee dryer, should such a dryer be employed.
Because of the aforementioned effects on strength and disruption of the papermaking process, considerable art has been devised to apply chemical softeners to already-dried paper webs either at the so-called dry end of the papermaking machine or in a separate converting operation subsequent to the papermaking step. Exemplary art from this field includes U.S. Pat. No. 5,215,626, issued to Ampulski, et. al. on Jun. 1, 1993; U.S. Pat. No. 5,246,545, issued to Ampulski, et. al. on Sep. 21, 1993; U.S. Pat. No. 5,525,345, issued to Warner, et. al. on Jun. 11, 1996, and U.S. patent application Ser. No. 09/053,319 filed in the name of Vinson, et al. on Apr. 1, 1998 all incorporated herein by reference. The U.S. Pat. No. 5,215,626 discloses a method for preparing soft tissue paper by applying a polysiloxane to a dry web. The U.S. Pat. No. 5,246,545 discloses a similar method utilizing a heated transfer surface. The Warner Patent discloses methods of application including roll coating and extrusion for applying particular compositions to the surface of a dry tissue web. Finally, the Vinson, et al. application discloses compositions that are particularly suitable for surface application onto a tissue web.
While each of these references represent advances over the previous so-called wet end methods, particularly with regard to eliminating the degrading effects on the papermaking process, there remains a need for providing a softening composition that has minimal effect on the strength properties of a tissue web. One of the most important physical properties related to softness is generally considered by those skilled in the art to be the strength of the web. Application of a softening composition generally causes a reduction in strength of a tissue web (Strength is the ability of the product, and its constituent webs, to maintain physical integrity and to resist tearing, bursting, and shredding under use conditions). This reduction is believed to result from a disruption of hydrogen bonds between the papermaking fibers that are formed as a result of the papermaking process. Achieving high softness without degrading strength has long been recognized as a means of providing improved tissue products.
Surface application of softening compositions has been found to be particularly useful in providing such softness improvements without substantially degrading the strength of the soft tissue paper product. For example, the parent of the present application discloses compositions that are particularly useful in providing such strong, softened tissue products. Thus, there is a continuing need for commercialization of such soft, strong tissue having a surface applied softening composition.
Commercial production of such strong, softened tissue offers particular challenges. For example, process operation and hygiene can be severely affected if the softening composition is not applied using a suitable process. As noted above with respect to U.S. Pat. No. 5,245,545, the art has applied softening compositions to certain of the rolls in the dry end of a paper machine for transfer to a web surface. While such roll application can successfully apply a softening composition to dried tissue, there are certain process risks. One such risk is roll wrapping in the event of a break in the web downstream of the applicator roll. When such a break occurs, there may be a substantial reduction in takeaway tension on the web at the applicator roll. On loss of takeaway tension, the softening composition can cause the web to adhere to the applicator roll because the takeaway tension is no longer available to overcome adhesive forces due to the softening composition. If such adhesion occurs, there is a high likelihood that the roll will wrap.
Spray application of the softening composition can overcome process operation issues, such as roll wrapping, because the softening composition can be applied to the web in a manner so there is little or no contact between the composition and process rolls before the composition has had a chance to set up. Spray application has its own set of issues, however. One such issue is that, while a minimum air pressure is required to create an spray pattern, there is also a maximum air pressure because particle aerosolization (i.e. creation of very small particles by the spray apparatus) increases with air pressure. The maximum air pressure is defined by the pressure where such aerosolization results in unacceptable line hygiene (i.e. too much of the softening composition is carried away from the web and deposits on process apparatus).
Accordingly, there is a continuing need for soft tissue paper products having good strength properties. There is also a need for improved softening compositions that can be applied to such tissue products to provide the requisite softness without unacceptably degrading the strength of the product or other important properties thereof. There is a further need for commercial processes capable of producing such products that have acceptable process operation and hygiene.
Such improved products, compositions, and processes are provided by the present invention as is shown in the following disclosure.
The present invention describes softening compositions that, when applied to tissue webs, preferably dried tissue webs, provide soft, strong, absorbent, and aesthetically pleasing tissue paper. The composition is a dispersion comprising:
an effective amount of a softening active ingredient;
a vehicle in which the softening active ingredient is dispersed;
an electrolyte dissolved in the vehicle, the electrolyte causing the viscosity of the composition to be less than the viscosity of a dispersion of the softening composition in the vehicle alone;
a bilayer disrupter to further reduce the viscosity of the softening composition; and
a low level of a high polymer that operates so as to increase the uniaxial and biaxial extensional viscosity of the composition without substantially affecting the shear viscosity thereof.
Reduced aerosolization through the use of this compound meaningfully widens the air pressure operating window for spray application thereof.
The amount of softening active applied to the tissue paper is preferably, between about 0.1% and about 10% based on the total weight of the softening composition compared to the total weight of the resulting tissue paper. The resulting tissue paper preferably has a basis weight of from about 10 to about 80 g/m2 and a fiber density of less than about 0.6 g/cc.
The term xe2x80x9cvehiclexe2x80x9d as used herein means a fluid that completely dissolves a chemical papermaking additive, or a fluid that is used to emulsify a chemical papermaking additive, or a fluid that is used to suspend a chemical papermaking additive. The vehicle may also serve as a carrier that contains a chemical additive or aids in the delivery of a chemical papermaking additive. All references are meant to be interchangeable and not limiting. The dispersion is the fluid containing the chemical papermaking additive. The term xe2x80x9cdispersionxe2x80x9d as used herein includes true solutions, suspensions, and emulsions. For purposes for this invention, all terms are interchangeable and not limiting. If the vehicle is water or an aqueous solution, then, preferably, the hot web is dried to a moisture level below its equilibrium moisture content (at standard conditions) before being contacted with the composition. However, this process is also applicable to tissue paper at or near its equilibrium moisture content as well.
All percentages, ratios and proportions herein are by weight, unless otherwise specified.